Electrically operated injection molding machine

ABSTRACT

An injection molding machine using a linear motion type electric motor (10, 20), as a drive source, is provided, which is simple and compact in construction. The linear motion type electric motor includes a non-magnetic shaft (21) on which yokes (22) and permanent magnets (23) are alternately fitted, and an annular stator (10) having an outer tube (11) within which cores (12) and printed type coils (13-18) are alternately disposed, the shaft extending through the stator. Upon supply of three-phase alternating currect to the coils, a screw of the injection molding machine coupled to the shaft is moved in unison with the shaft to thereby perform injection operation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an injection molding machine having adrive source which is of a linear motion type electric motor.

2. Description of the Related Art

An injection molding machine includes various mechanisms such as aninjection mechanism for axially moving a screw to perform injectionoperation, a clamping mechanism for opening, closing and clamping molds,an ejector mechanism for axially moving an ejector pin to extrude amolded product, and a nozzle touch mechanism for touching a nozzle tothe mold. Each of these mechanisms has its axis (hereinafter referred toas linear motion member) arranged to be linearly driven. A screw is anexample of such a linear motion member.

In a hydraulically operated injection molding machine, it is easy tocause linear motion of these linear motion members, by driving themembers with a hydraulic cylinder. On the other hand, in a conventionalelectrically operated injection molding machine, a rotational output ofan electric motor is converted into a driving force (hereinafterreferred to as linear driving force) which acts on the associated linearmotion member in the direction along which the same member moves. Thisis done with a conversion mechanism, such as a ball screw and nut, sothat the linear motion member is moved by the linear driving force.

In this manner, a conventional injection molding machine requires aconversion mechanism, and is hence complicated in construction and highin cost. Moreover, it requires space for installation of the conversionmechanism, and has the drawback that the whole arrangement becomes largein size.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an injection moldingmachine which is simple and compact in construction and is low-priced.

In order to achieve the above-mentioned object, an injection moldingmachine according to the present invention includes a linear motionmember arranged to be linearly movable relative to a main body of theinjection molding machine, and a linear motion type electric motorsupported by the main body of the molding machine. Further, the linearmotion member is coupled to a movable portion of the motor in a mannerso as to be movable in unison with the movable portion which is arrangedto be linearly movable relative to a stationary portion of the motor.

As mentioned above, according to the present invention, since the linearmotion type electric motor is employed as the drive source of the linearmotion member, no conversion mechanism for converting rotational drivingforce into linear driving force is required. As a result, an injectionmolding machine can be provided, which is simple and compact inconstruction and low in cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an essential portion of an injectionmolding machine according to an embodiment of the present invention;

FIG. 2 is a fragmentary perspective view showing a linear motion typeelectric motor of the FIG. 1 embodiment;

FIG. 3 is a fragmentary schematic longitudinal section view showing themotor of FIG. 2;

FIG. 4 is a diagram showing a waveform of a three-phase alternatingcurrent supplied to the motor;

FIG. 5A is a view explaining a positional relationship between a statorof the linear motor and a movable section of the motor;

FIG. 5B is a diagram showing waveforms of an electric current flowingthrough the stator, magnetic field generated by the current, andmagnetic field generated by the movable section, when the positionalrelationship of FIG. 5A is assumed;

FIG. 6A is a view showing a different positional relationship betweenthe stator and the movable section;

FIG. 6B is a diagram showing a waveform associated with the positonalrelationship of FIG. 6A;

FIG. 7A is a view explaining a further different positionalrelationship; and

FIG. 7B is a diagram showing a waveform associated with the positionalrelationship of FIG. 7A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an injection molding machine according to an embodiment ofthe present invention, which employs a linear motion type electric motor(hereinafter referred to as linear motor) as a drive source of aninjection mechanism. Reference numeral 10 designates an annular statorwhich forms one half of the linear motor and is fixed to a base B of theinjection molding machine. Reference numeral 20 denotes a movablesection or armature forming the other half of the linear motor, whichextends through a central hollow portion of the stator 10. The movablesection 20 has a shaft 21 having one end fixed to a screw shaft 31 of ascrew 30 by means of fixture means 70, and another end fixed to a splineshaft 60 by means of fixture means 80. A tubular member 51 isspline-connected to a spline groove 61 formed in the spline shaft 60which is arranged to be rotatable in unison with the tubular member 51and axially movable relative to the later member.

A rotary drive member 50 is formed with a central stepped hole 52 havinga large diameter portion to which the tubular member 51 is fitted sothat the member 51 is rotatable in unison with the member 50. The hole52 has a small diameter portion through which the spline shaft 60 isloosely inserted. Further, the rotary drive member 50 is coupled througha fixture means 90 to a motor shaft 41 of a screw rotation motor 40 forrotating the screw 30.

With reference to FIGS. 2 and 3, a further explanation of the linearmotor will be given.

The stator 10 of the linear motor includes an outer tube 11, a pluralityof annular cores 12 and a plurality of printed type annular coils 13through 18. The outer tube is made of a soft magnetic material (mildsteel, for instance), and the printed coils 13 through 18 each have apredetermined inner diameter and are fittedly mounted in the outer tube11. The cores 12 are made of a soft magnetic material (mild steel, forinstance), and preferably each have the same inner diameter as that ofthe printed coils 13 through 18 and are fitted in the outer tube 11.Further, the cores 12 have outer peripheral surfaces which are formedwith grooves (not shown) extending in the axial direction of the cores,so that lead wires (not shown) are disposed in the grooves forconnecting associated ones of the printed coils 13 through 18 to eachother and connecting a three-phase A.C. power supply (not shown) withassociated coils.

The outer tube 11, the cores 12 and the printed coils 13 through 18 areseparately fabricated beforehand. During assembly, the cores 12, whichnumber seven in the illustrated embodiment, and the printed coils 13through 18 are disposed alternately within the interior of the outertube 11. Two lead wires of each printed coil 13 through 18 are drawn outto the outside through the grooves of the cores 12. Finally, the cores12 disposed at opposite sides are connected to the outer tube 11 bymeans of a shrinkage fit, for instance. In the meantime, a mount member19 is fixed to the stator 10 for connecting the stator 10 to the base Bof the injection molding machine.

The movable section 20 includes the shaft 21, a plurality of annularyokes (part of which is shown by reference numeral 22), and a pluralityof annular permanent magnets (part of which is shown by referencenumerals 23, 24, 25 and 26). The shaft 21 is composed of a non-magneticmaterial, and the yokes 22 each have an outer diameter which is slightlysmaller than the inner diameter of the stator 10, and are fitted on theshaft 21. Preferably, the permanent magnets 23, 24, 25, 26, each havethe same outer diameter as that of the yokes 22, and are fitted on theshaft 21. Respective lengths of the yokes 22 and the permanent magnets23, 24, 25, 26, are set beforehand to values sufficient to permit themagnets and the coil unit to achieve a desired electromagnetic function(described later).

The shaft 21, the yokes 22 and the permanent magnets 23, 24, 25, 26, areseparately fabricated beforehand. When assembled, the yokes 22 and thepermanent magnets 23, 24, 25, 26, are alternately disposed on the outerperiphery of the shaft 21 over a length which is larger than a desiredmoving stroke of the movable section 20 in such a manner that theadjacent permanent magnets are disposed oppositely in their polarity. Inthis case, the adjacent yokes 22 are magnetized in a manner having the Npole and the S pole, respectively.

The printed coil pairs 13, 16; 14, 17; 15, 18 are connected to U-, W-and V-phases of the three-phase alternating current (see, FIG. 4),respectively. In addition, as shown in FIGS. 5-7, the respective leadwires are connected to the three-phase A.C. power supply so thatelectric current flows in opposite directions between the two coilsforming as associated one of the printed coil pair.

Referring to FIG. 4 through FIG. 7, a further explanation will be givenas to the case where the linear motor is driven to perform injectionoperation.

First, it is assumed that the stator 10 and the armature 20 assume theirpositional relationship shown in FIG. 5A and the three-phase alternatingcurrent shown in FIG. 4 is supplied to the respective printed coils 13through 18. At the time point of t1, U=1, W=-(1/2) and V=-(1/2), thatis, electric current of 100% flows in the printed coil (+U) 13, andelectric current of 50% flows in the printed coil (-W) 14, and electriccurrent of -50% flows in the printed coil (+V) 15, respectively.Similarly, electric current of -100%, -50% and 50% flows through coils(-U), (+W) and (-V), respectively. That is, electric current flowingthrough the printed coils 13 through 18 has a stair step waveform A, asshown in FIG. 5B, and a totally averaged waveform corresponding to thewaveform A is indicated by B which is shown by dotted line. Further,magnetic field generated by this electric current waveform B isindicated by a waveform C which is shifted in phase from the electriccurrent distribution.

On the other hand, magnetic field generated by the permanent magnets 24through 26 is shown by a waveform D. Accordingly, as apparent from arelative phase relationship of waveforms C and D shown in FIG. 5B, the Spole of waveform D is repulsive from the S pole of waveform C but isattractive to the N pole of waveform C, and the N pole of waveform D isrepulsive from the N pole of waveform C. As a result, the movablesection 20 which is movable relative to the stator 10 is moved right, asshown by an arrow. In this manner, the positional relationship shown inFIG. 6A is reached.

At the time point of t2, electric current flowing through the printedcoils 13 through 18, average electric current, magnetic field generatedby the average current, and magnetic field generated by the permanentmagnets 24 through 26 are indicated in FIG. 6B by waveforms A, B, C, andD, respectively. As apparent from the relative positional relationshipbetween the waveforms C and D, the armature 20 is moved right, as shownby an arrow. In this manner, the positional relationship shown in FIG.7A is reached.

Next, at the time point of t3, electric current flowing through theprinted coils 13 through 18, average electric current, magnetic fieldgenerated by the average current, and magnetic field generated by thepermanent magnets 25 through 27 are indicated in FIG. 7B by waveforms A,B, C, and D, respectively. As apparent from the relative positionalrelationship between the waveforms C and D, the armature 20 is movedright, as shown by an arrow.

As apparent from the foregoing explanation, the movable section 20 andhence the shaft 21 are linearly moved by supplying a three-phasealternating current to the respective printed coils 13 through 18, so asto move the screw 30 in the forward direction (to the right in FIG. 1),thereby performing an injection operation.

During a metering operation, the screw rotating motor 40 is driven torotate the shaft 21 of the movable section 20 which is coupled throughrotary drive member 50, outer tube 51 and spline shaft 60 to the motor40 in a manner to be rotatable in unison therewith, so as to rotate thescrew 30. At this time, weak electric current may be supplied to theprinted coils 13 through 18 of the stator 10 of the linear motor, toapply a predetermined back pressure to molten resin.

In the above-mentioned embodiment, the case using the linear motor ofsynchronous type has been explained. Alternatively, an induction typelinear motor may be employed. In this case, a shaft made of a softmagnetic material and an electrically conductive member are employed inplace of the non-magnetic shaft 21 and the permanent magnets 23, 24, 25,26, in the arrangement shown in FIGS. 2 and 3. In the case of using aninduction motor, it is unnecessary to dispose annular electricallyconductive members and annular yokes in phase with the printed coils 13through 18.

A linear motor is employed as the drive source for injection axis foraxially driving the screw, in the above-mentioned embodiment. Similarly,linear motors may be used as drive sources for linear motion mechanismssuch as clamping mechanism, ejector and nozzle touch mechanism, toeliminate conversion mechanisms for converting rotary motion into linearmotion to simplify the whole arrangement, as explained above. Inparticular, it is advantageous to construct the drive source for axiallydriving the screw by the above-mentioned type of cylindrical linearmotor because this makes it possible to achieve the axial and rotarymotions of the screw with a simple structure.

We claim:
 1. An injection molding machine having an injection mechanism,a mold clamping mechanism, an ejector, and a nozzle touch mechanism,each including a linear motion member which is linearly movable,comprising:at least one linear motion electric motor having a stationarysection and a movable section which is linearly movable relative to saidstationary section; and means for operatively coupling each said movablesection of said at least one linear motion electric motor to acorresponding one of said linear motion members of the injectionmechanism, the mold clamping mechanism, the ejector, and the nozzletouch mechanism, so as to be movable in unison with said correspondinglinear motion member.
 2. An injection molding machine according to claim1, wherein said linear motion electric motor is a synchronous electricmotor having a field system and an armature, one of the movable andstationary sections of said linear motion electric motor being formed bysaid field system, and the other section being formed by said armature.3. An injection molding machine according to claim 2, further comprisinga base, the linear motion member being linearly movable relative to thebase.
 4. An injection molding machine according to claim 2, wherein thelinear motion member is a screw.
 5. An injection molding machineaccording to claim 2, wherein said linear motion electric motor is aninduction electric motor having a field system and an electricallyconductive member, one of the movable and stationary sections of saidlinear motion electric motor being formed by said field system, and theother section being formed by said electrically conductive member.
 6. Aninjection molding machine according to claim 2, wherein said linearmotion electric motor includes a non-magnetic shaft, a plurality ofannular yokes and annular permanent magnets alternately fitted on and inan axial direction of the shaft, a tubular structure through which theshaft is loosely inserted, said tubular structure having an outer tubemade of a soft magnetic material, and a plurality of annular cores andannular printed coils alternately disposed in the outer tube in an axialdirection of the tubular structure, one of the movable and stationarysections of said linear motion electric motor being formed by said shaftand the other section being formed by said tubular structure.
 7. Aninjection molding machine according to claim 6, wherein the injectionmolding machine includes an injection mechanism having a screw, saidscrew being the linear motion member, and being coupled to saidnon-magnetic shaft of said linear motion electric motor.
 8. An injectionmolding machine according to claim 1, wherein said linear motionelectric motor is an induction electric motor having a field system andan electrically conductive member, one of the movable and stationarysections of said linear motion electric motor being formed by said fieldsystem, and the other section being formed by said electricallyconductive member.
 9. An injection molding machine according to claim 1,wherein said linear motion electric motor includes a non-magnetic shaft,a plurality of annular yokes and annular permanent magnets alternatelyfitted on and in an axial direction of the shaft, a tubular structurethrough which the shaft is loosely inserted, said tubular structurehaving an outer tube made of a soft magnetic material, and a pluralityof annular cores and annular printed type coils alternately disposed inthe outer tube in an axial direction of the tubular structure, one ofthe movable and stationary sections of said linear motion electric motorbeing formed by said shaft and the other section being formed by saidtubular structure.
 10. An injection molding machine according to claim9, wherein the injection molding machine includes an injection mechanismhaving a screw, said screw being the linear motion member, and beingcoupled to said non-magnetic shaft of said linear motion electric motor.11. An injection molding machine according to claim 1, furthercomprising a base, the linear motion member being linearly movablerelative to the base.
 12. An injection molding machine according toclaim 1, wherein the linear motion member is a screw.
 13. An injectionmolding machine having an injection mechanism including a screw which isdisposed for rotation about an axis and for linear movement along saidaxis, said injection mechanism comprising:an electric motor for rotatingthe screw; means for operatively coupling the screw to said electricmotor; a linear motion electric motor having a stationary section and amovable section which is linearly movable relative to said stationarysection; and means for operatively coupling the screw to said movablesection of said linear motion electric motor so as to be movable inunison with said movable section.
 14. An injection molding machineaccording to claim 13, wherein said linear motion electric motor is asynchronous electric motor having a field system and an armature, one ofthe movable and stationary sections of said linear motion electric motorbeing formed by said field system, and the other secton being formed bysaid armature.
 15. A drive unit for an injection molding machine havinga stationary base portion, comprising:a linear motion member which islinearly movable relative to the stationary base portion of theinjection molding machine; and a linear motion electric motor having astationary section supported by the stationary base portion of theinjection molding machine and a movable section which is linearlymovable relative to the stationary section, said linear motion memberbeing coupled to the movable section of said linear motion electricmotor and being operable to axially drive the movable section.
 16. Adrive unit for an injection molding machine according to claim 15,wherein said linear motion electric motor is a synchronous electricmotor having a field system and an armature, one of the movable andstationary sections of said linear motion electric motor being formed bysaid field system, and the other section being formed by said armature.17. A drive unit for the injection molding machine according to claim15, wherein said linear motion electric motor is an induction electricmotor having a field system and an electrically conductive member, oneof the movable and stationary sections of said linear motion typeelectric motor being formed by said field system, and the other sectionbeing formed by said electrically conductive member.
 18. A drive unitfor an injection molding machine according to claim 15, furthercomprising means operatively coupled to the movable section of theelectric motor for rotating the movable section, wherein the linearmotion member is a screw.
 19. A drive unit for an injection moldingmachine according to claim 15, wherein said linear motion electric motorincludes a non-magnetic shaft, a plurality of annular yokes and annularpermanent magnets alternately fitted on and in an axial direction of theshaft, a tubular structure through which the shaft is loosely inserted,said tubular structure having an outer tube made of a soft magneticmaterial, and a plurality of annular cores and annular printed coilsalternately disposed in the outer tube in an axial direction of thetubular structure, one of the movable and stationary sections of saidlinear motion electric motor being formed by said shaft and the othersection being formed by said tubular structure.
 20. A drive unit for aninjection molding machine according to claim 19, wherein the injectionmolding machine includes an injection mechanism having a screw, saidscrew being the linear motion member, and being coupled to saidnon-magnetic shaft of said linear motion electric motor.